Rotating shaft scavenging scoop

ABSTRACT

A bearing scavenge system comprises a scavenging passage extending axially through a rotating shaft supported by the bearing assembly. Oil and air are drawn from an oil cavity of the bearing assembly and evacuated through the rotating shaft as the shaft rotates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of Ser. No. 10/802,830, now U.S. Pat.No. 7,124,857 filed Mar. 18, 2004 and issued on Oct. 24, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to gas turbine engines and, moreparticularly, to oil scavenging systems.

2. Description of the Prior Art

Proper scavenging of used oil in bearing assemblies is essential toprevent overheating and premature wear of gas turbine engine mechanicalparts. The used oil is usually circulated to an oil treatment system toremove air and particles therefrom before being returned to the bearingassemblies.

Oil scavenging systems typically rely on a simple pressure imbalance todirect the used oil into collection tubes for transport to a main oilpump of the oil treatment system. More efficient systems have beendevised, employing special pumps or spinning vanes to improve the usedoil circulation. However, such special pumps and vanes increase theweight of the engine and thus the costs of operation.

Accordingly, there is a need for an efficient scavenge system for abearing assembly that has a minimal weight.

SUMMARY OF THE INVENTION

It is therefore an aim of the present invention to provide an improvedscavenge system for a bearing assembly of a gas turbine engine.

Therefore, in accordance with a general feature of the presentinvention, there is provided a scavenge system for a bearing assembly,the system comprising a scavenging passage extending axially through arotating shaft supported by the bearing assembly, and at least one scoopprovided on the rotating shaft, said at least one scoop impelling oilinternally of said rotating shaft into said scavenging passage as saidat least one scoop rotates with said rotating shaft.

In accordance with a further general aspect of the present invention,there is provided a scavenge system for a bearing assembly, the systemcomprising a scavenging passage extending axially through a rotatingshaft supported by the bearing assembly, and means provided on therotating shaft for drawing oil internally of said rotating shaft intosaid scavenging passage as said shaft rotates.

In accordance with a further general aspect of the present invention,there is provided a gas turbine engine comprising a compressor section,a combustor and a turbine section in serial flow communication with oneanother, a main rotating shaft supported by a bearing assembly, and ascavenge system for the bearing assembly, the scavenge system comprisinga scavenging passage extending axially through said main rotating shaft,and at least one inlet hole defined in said main rotating shaft and inflow communication with said scavenging passage, said at least one inlethole extending at an angle to a radius of the main rotating shaft tothereby cause oil about the rotating shaft to be drawn into saidscavenging passage in said main shaft via said at least one inlet holeas said main shaft rotates.

Also in accordance with another general aspect of the present invention,there is provided a scavenge system for a bearing assembly supporting arotating shaft in a gas turbine engine, the system comprising firstfluid communication means between a lubricant cavity containing thebearing assembly and an annular inner surface closely surrounding anouter surface of the rotating shaft, second fluid communication meanswithin the rotating shaft communicating with a stationary chamber, andthird fluid communication means between the outer surface of therotating shaft and the second fluid communication means, the third fluidcommunication means being defined such as to communicate with the firstfluid communication means during at least a portion of a rotation of theshaft, and such that the rotation of the shaft causes used lubricantcoming from the lubricant cavity to be moved from the first fluidcommunication means to the third fluid communication means so as todeliver the used lubricant to the stationary chamber through the secondfluid communication means.

In accordance with a still further general aspect of the presentinvention, there is provided a method of evacuating scavenge air and oilfrom a bearing assembly supporting a main shaft of a gas turbine engine,the method comprising the steps of: a) feeding the scavenge air and oilfrom the bearing assembly to an interface with said main shaft, b)drawing the scavenge air and oil from said interface into said mainshaft, and c) evacuating the oil axially through said main shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, showing by wayof illustration a preferred embodiment of the invention and in which:

FIG. 1 is a schematic side view of a gas turbine engine, in partialcross-section, to which an embodiment of the present invention isapplied;

FIG. 2 is a cross-sectional side view showing bearing assembliessupporting a rotating shaft of the gas turbine engine of FIG. 1; and

FIG. 3 is a cross-sectional view of a scavenge system taken along linesB-B of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. A rotating shaft 20 extendswithin the engine 10 and transfers energy from the turbine section 18 tothe compressor 14 and the fan 12.

Referring to FIG. 2, the rotating shaft 20 is supported by a pluralityof annular bearing assemblies 22, as well known in the art. Each annularbearing assembly 22 comprises a series of roller bearings 24 located ina bearing compartment 26. The bearing compartment 26 is defined suchthat each bearing assembly 22 is located within an annular oil cavity28. The annular oil cavity 28 contains oil providing adequatelubrication to the bearing assembly 22.

During use, used oil from the oil cavity 28 is circulated to an oiltreatment system (not shown) in order to remove unwanted debris and airfrom the used oil. A scavenge system 40 is used to direct the mixture ofair and oil from the oil cavity 28 to the oil treatment system. Thescavenge system 40 is illustrated in FIGS. 2-3 and will be described inthe following.

In the bearing compartment 26, a series of axial tubes 50 extend alongan axial direction of the rotating shaft 20, and a series of radialtubes 48 extend along a radial direction relative to the rotating shaft20. Each axial tube 50 has one end connected to one end of acorresponding radial tube 48. The opposed end of each axial tube 50 isin fluid communication with the oil cavity 28. The opposed end of eachradial tube 48 defines an opening 51 in an inner annular surface of thebearing assembly 22 which closely surrounds the rotating shaft 20. Theopenings 51 are distributed along a circumference of the inner annularsurface.

The combination of each axial tube 50 with the corresponding radial tube48 forms a conduit going from the oil cavity 28 to an opening 51 at theinterface between the bearing compartment 26 and the rotating shaft 20.

An annular channel 42 is defined within the rotating shaft 20 and isconcentric therewith. A plurality of holes 44 are defined around acircumference of an outer surface of the rotating shaft 20. The holes 44are in fluid communication with the annular channel 42. The holes 44 arepreferably perpendicular to the annular channel 42 and defined at alarge angle with respect to a radius of the rotating shaft 20. The holes44 are machined so that the remaining shaft material between adjacentholes forms a curved scoop 46. The holes 44 are located in the samediametrical plane as the openings 51, such that each hole 44 can bealigned in turn with each opening 51 and be in fluid communicationtherewith during the rotation of the shaft 20.

The scoops 46 preferably have a curved section, and are progressivelythinner toward the outer surface of the shaft 20. As such, they have aprofile which is similar to an airfoil. The scoops 46 are curved in thedirection of rotation of the shaft 20 as depicted by arrow 47 in FIG. 3.A space between adjacent scoops 46, which is curved and thinner towardthe center of the shaft 20, defines the shape of the holes 44. The shapeand angle of the holes 44 and scoops 46 minimizes the effects of thecentrifugal forces acting to push the air and oil mixture away from theshaft 20. Thus, a rotation of the holes 44 and scoops 46 brought by therotation of the shaft 20 will “pick up” and draw the air and oil mixturecoming from the openings 51 to bring it to the annular channel 42through the holes 44.

Because the angle of the holes 44 with respect to the radial directionof the shaft 20 is preferably large, the number of holes 44 and scoops46 is preferably limited to three. As illustrated in FIG. 3, a preferredembodiment of the scavenge system 40 includes three groups having eachthree radial tubes 48 and axial tubes 50 defined in proximity to oneanother such as to have a common opening 51 for each group. The holes44, scoops 46 and groups of tubes 48, 50, are all equally angularlyspaced apart in order to provide a balanced scavenge system 40.

Thus, the mixture of air and oil can be transported from the oil cavity28 to the openings 51 at the interface between the bearing compartment26 and the rotating shaft 20, then from the openings 51 to the holes 44.The mixture then travels along the annular channel 42 to an extremitythereof which extends such as to define an annular exit port at the endof the shaft 20. This exist port provides fluid communication betweenthe annular channel 42 and a stationary chamber 52 located at thedownstream end of the shaft 20, where the mixture is collected. Pipes 54provide fluid communication between the chamber 52 and an oil treatmentsystem. A sufficient pressure gradient ensures that the air and oilmixture will circulate adequately from the oil cavity 28 to the oiltreatment system following arrow 56. The following treatment of the airand oil mixture and subsequent return of the cleaned oil to the oilcavity 28 is well known in the art and as such will not be discussedherein.

In an alternate embodiment, it is contemplated to replace the chamber 52located at the end of the shaft 20 by an annular stationary chamberlocated around the rotating shaft 20 and in fluid communication with thechannel 42 through a series of radial holes. In this case, thecentrifugal forces acting on the used oil propels it from the channel 42to the annular chamber, where it can be led to the oil treatment systemthrough appropriate piping.

The scavenge system 40 can also be used with other types of bearingassemblies supporting a rotating shaft, and as such should not beconstrued as being limited to aircraft engines.

The scavenge system 40 uses a channel 42 which is directly machinewithin the shaft, and scoops 46 are preferably formed by removingmaterial from the rotating shaft 20 in order to machine the holes 44.Thus, these components reduce the weight of the rotating shaft ratherthan increase the overall engine weight, as added components would. Thescavenge system 40 therefore has the advantage of representing a minimalweight increase for the engine.

It is understood that the present invention applies to any gas turbineengines, and in fact to any rotating machinery in which oil isscavenged.

The embodiments of the invention described above are intended to beexemplary. Those skilled in the art will therefore appreciate that theforgoing description is illustrative only, and that various alternativesand modifications can be devised without departing from the spirit ofthe present invention. Accordingly, the present is intended to embraceall such alternatives, modifications and variances which fall within thescope of the appended claims.

1. A method of evacuating scavenge air and oil from a bearing assemblysupporting a main hollow shaft of a gas turbine engine, the methodcomprising the steps of: a) feeding the scavenge air and oil from thebearing assembly to an interface with said main hollow shaft, b) drawingthe scavenge air and oil from said interface radially inwardly into saidmain hollow shaft, and c) evacuating the oil axially internally throughsaid main hollow shaft.
 2. A method as defined in claim 1, wherein stepa) comprises the steps of: defining a plurality of circumferentiallyaligned openings in an annular surface of a bearing compartment, theannular surface being located at the interface between the bearingcompartment and the main shaft, and providing fluid communicationbetween the bearing compartment and the openings.
 3. A method as definedin claim 2, wherein step b) comprises the steps of: defining a pluralityof circumferentially aligned holes in the rotating shaft at theinterface, the holes being defined such as to create an interactionbetween the holes and the openings which draws the air and oil radiallyinwardly from the openings to the holes upon rotation of the main shaft.4. A method as defined in claim 3, wherein step c) comprises the stepsof: providing fluid communication within the main shaft from the holesto a stationary chamber; and rotating the main shaft so as to producethe interaction between the holes and the openings such that the air andoil are moved from the bearing compartment to the stationary chamber. 5.A method as defined in claim 1, wherein step b) comprises scooping theoil with at least one scoop defined on said hollow shaft.
 6. A method asdefined in claim 5, comprising directing the oil at a surface closelysurrounding the hollow shaft and scooping the oil from the surface asthe shaft is rotated.